1. Field of the Invention
The present invention generally relates to an electric discharge shaping/profiling machine such as a die sinking electric discharge machine, an electric spark machine or the like for shaping or profiling (i.e., machining in more general terms) a workpiece by applying a pulse-like voltage across an electrode and the workpiece between which a processing liquid or solution such as a dielectric liquid intervenes. More particularly, the present invention is concerned with a jump control apparatus for the electric discharge shaping/profiling machine, which apparatus is designed for improving the precision of machining (or machining precision) while allowing the time taken for the machining process to be shortened essentially without being influenced by geometrical factors such as shape or profile to be finally imparted to the workpiece.
2. Description of Related Art
In the electrical discharge shaping/profiling machine such as the die sinking electric discharge machine or the like employed heretofore for shaping or profiling a workpiece such as a die or the like, a high-frequency electrical spark is discharged from a metal tool serving as a tool electrode to disintegrate electrically conductive materials from a workpiece such as of hardened steel or the like. The tool electrode and the workpiece are immersed in a dielectric liquid (processing liquid), and a feed mechanism maintains a spark gap between the tool electrode and the workpiece. As spark discharges melt the materials of the workpiece, the particles are flushed away, and the tool electrode advances. The process is accurate and is used for machining dies, molds, holes, slots, and/or cavities of almost any desired shape.
In the electric discharge shaping/profiling machine of this type, the tool electrode and the workpiece are immersed in the processing liquid so that the liquid intervenes between the tool electrode and the workpiece. This is for the purpose of suppressing temperature-rise at a location where the electric discharge takes place to thereby prevent occurrence of accident such as misfire due to the discharge spark.
In the course of the electric discharge machining, sludge (i.e., pulverized materials or particulates) is produced from a surface of the workpiece being machined. If the sludge should be left as it is, performance of the electric discharge taking place between the tool electrode and the workpiece will be lowered, involving degradation in the precision of machining. For this reason, it is required to remove or discharge the sludge as speedily and timely as possible.
Such being the circumstances, there has heretofore been proposed a jump control apparatus for moving upwardly and downwardly the tool electrode of the electric discharge shaping/profiling machine in succession to the pulse-like electric discharge to thereby remove or discharge the sludge produced during the machining process substantially on a real time basis.
With this type of the jump control apparatus for the electric discharge shaping/profiling machine, when the tool electrode is moved downwardly relative to the surface of the workpiece being machined, the dielectric liquid or processing liquid intervening between the tool electrode and the workpiece is caused to forcibly flow onto the surface of the workpiece being machined, whereby the sludge is caused to be flushed away from the surface of the workpiece being machined.
In this conjunction, it is however noted that in case the jumping velocity of the tool electrode is smaller than the optimal value, the amount of the processing liquid which is displaced from the surface of the workpiece being machined will decrease. As a result of this, when the tool electrode is moved upwardly, the liquid containing the sludge again flows back onto the surface of the workpiece being machined, rendering it difficult or impossible to remove the sludge.
Such being the circumstances, in order to allow the sludge to be removed speedily and effectively, it is required to set optimally the so-called jump conditions (e.g. jump-up quantity and jumping velocity) for the tool electrode by taking into consideration not only the properties of the processing liquid such as viscosity but also mechanical factors (e.g. mechanical strength) of a main spindle employed for driving the tool electrode.
As the hitherto known jump control apparatus for the electric discharge shaping/profiling machine, there may be mentioned those disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 309630/1998 (JP-A-10-309630) and Japanese Patent Application Laid-Open Publication No. 200 1-9642 (JP-A-2001 -9642), respectively.
In the case of the jump control apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 309630/1998, the jump-up quantity is determined on the basis of the area of the workpiece being machined, depth thereof and the like factors, whereon the jumping velocity is automatically set through a fuzzy logic or inference on the basis of the area being machined and the spark gap in precedence to initiation of the jump control.
However, in the case of the jump control apparatus described just above, it is noted that upon setting the jump conditions, no consideration is paid to the change or variation which may occur in the distance (spark gap) between the tool electrode and the workpiece in dependence on the conditions for the electric discharge as well as in the machined-surface length between the machining surface defined at the tip end of the tool electrode (i.e., bottom surface of the tool electrode) and the top surface of the workpiece.
Consequently, when the distance between the tool electrode and the workpiece (i.e., one of the conditions for the electric discharge) is set to be large and/or when the shape or profile resulting from the machining presents a tapered portion and/or a curved surface, it is difficult or impossible to remove the sludge by flushing with the processing liquid.
As a result of this, such situation may arise that the machining process for the workpiece does not proceed speedily and smoothly. Besides, the desired machining precision may not satisfactorily be achieved.
Further, in the jump control apparatus described above, the jump conditions are set or established through the fuzzy logic inference. Consequently, in the case where the tool electrode is of a rib-like form (i.e., when the desired finished shape of the workpiece is of a rib-like form), which means that the area subjected to the machining process is large, the jump-up quantity of the tool electrode may be estimated or inferred to be smaller than the demanded or desired value.
However, for discharging or removing the sludge by flushing with the processing liquid carrying the sludge, a large jump-up quantity is ordinarily demanded. Accordingly, with the small jump-up quantity such as mentioned above, there may arise such unwanted situation that the sludge can not adequately be removed.
On the other hand, in the jump control apparatus for the electric discharge shaping/profiling machine disclosed in Japanese Patent Application Laid-Open Publication No. 2001-9642 (JP-A-2001-9642), the feeding speed for the jump motion of the tool electrode is set to 20 m/min at the lowest, while the tool electrode feeding acceleration/deceleration is set to be not lower than 1.0 G.
In this case, however, since the moving speed of the tool electrode may be set to a value greater than a permissible value, there may take place a region of negative pressure at or along the bottom surface of the tool electrode when it moves upwardly, as a result of which mechanical damage and degradation of the machining precision may unwantedly occur due to deformation of the main spindle, giving rise to a problem.
It is further noted that in the apparatus disclosed in both the publications cited above, a feed-back control system is adopted for controlling optimally the jump conditions stepwise progressively in the course of the machining process. As a consequence, a lot of time is required for validating actually the optimal values for the jump conditions for removing the sludge, which may ultimately incur degradation of the machining precision, to another disadvantage.
As will now be appreciated from the foregoing, with the hitherto known or conventional jump control apparatus for electric discharge shaping/profiling machines such as a die sinking electric discharge machine or the like, no consideration is given to the important working or machining conditions upon setting the jump conditions for the removal of the sludge. Besides, the jump conditions are put into effect by making use of feed-back control. Consequently, it is difficult or even impossible to optimize the jump conditions speedily and timely in the course of the machining process, giving rise to a problem that the desired machining precision cannot be satisfactorily achieved.
In the light of the state of the art described above, it is an object of the present invention to provide a jump control apparatus for an electric discharge shaping/profiling machine such as a die sinking electric discharge machine, which apparatus can evade from the drawbacks and problems of the conventional apparatuses such as mentioned above and which apparatus allows the machining precision to be significantly improved or enhanced while ensuring remarkable reduction of the machining or processing time by removing the sludge speedily and satisfactorily regardless of differences in the shape or profile among the workpieces subjected to the machining process by adopting a feed-forward control for setting the jump conditions in precedence to execution of the machining process.
A second object of the present invention is to provide a jump control apparatus for an electric discharge shaping/profiling machine such as a die sinking electric discharge machine, which is capable of reducing the process or machining time while improving the machining precision notwithstanding of differences in shape among workpieces subjected to the processing by inferring or estimating the jump conditions on the basis of the working or machining conditions which play important roles in determining the jump conditions.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a first aspect of the present invention a jump control apparatus for an electric discharge shaping/profiling machine designed for machining a workpiece by applying a pulse-like voltage across a tool electrode mounted on a main spindle at one end thereof and the workpiece disposed in opposition to the tool electrode with a processing liquid intervening therebetween. The apparatus includes a feed control unit for controlling a feed quantity of the main spindle to thereby control a vertical position of the tool electrode relative to the workpiece, a jump condition estimating unit for estimating jump conditions for effectuating jump motion of the tool electrode with a view to discharging sludge taking place between the tool electrode and the workpiece in the course of machining process performed for the workpiece, the jump conditions as generated being then inputted to the feed control unit, an input unit for allowing machining conditions bearing relation to the jump conditions to be inputted in precedence to machining process to be performed for the workpiece, and a numerical control unit for determining arithmetically various parameters in dependence on the machining conditions to thereby input the various parameters as determined to the jump condition estimating unit. In the apparatus described above, the jump condition estimating unit is so designed as to estimate the jump conditions on the basis of a feed-forward control effectuated by making use of the various parameters mentioned above.
According to a second aspect of the invention, there is provided a jump control apparatus for an electric discharge shaping/profiling machine designed for machining a workpiece by applying a pulse-like voltage across a tool electrode mounted on a main spindle at one end thereof and the workpiece disposed in opposition to the tool electrode with a processing liquid intervening therebetween. The apparatus includes a feed control unit for controlling a feed quantity of the main spindle to thereby control a vertical position of the tool electrode relative to the workpiece, a jump condition estimating unit for estimating jump conditions for effectuating jump motion of the tool electrode with a view to discharging sludge taking place between the tool electrode and the workpiece in the course of machining process performed for the workpiece, the jump conditions as generated being then inputted to the feed control unit, an input unit for allowing machining conditions bearing relation to the jump conditions to be inputted in precedence to machining process to be performed for the workpiece, and a numerical control unit for determining arithmetically various parameters in dependence on the machining conditions to thereby input the various parameters as determined to the jump condition estimating unit. In the apparatus described above, the jump condition estimating unit is so designed as to estimate the jump conditions on the basis of the various parameters in precedence to machining of the workpiece.
According to a third aspect of the invention, there is provided a jump control apparatus for an electric discharge shaping/profiling machine designed for machining a workpiece by applying a pulse-like voltage across a tool electrode mounted on a main spindle at one end thereof and the workpiece disposed in opposition to the tool electrode with a processing liquid intervening therebetween. The apparatus includes a feed control unit for controlling a feed quantity of the main spindle to thereby control a vertical position of the tool electrode relative to the workpiece, a jump condition estimating unit for estimating jump conditions for effectuating jump motion of the tool electrode with a view to discharging sludge taking place between the tool electrode and the workpiece in the course of machining process performed for the workpiece, the jump conditions as generated being then inputted to the feed control unit, an input unit for allowing machining conditions bearing relation to the jump conditions to be inputted in precedence to machining process to be performed for the workpiece, and a numerical control unit for determining arithmetically various parameters in dependence on the machining conditions to thereby input the various parameters as determined to the jump condition estimating unit. In the apparatus described above, the jump condition estimating unit is so designed as to determine desired values for the jump conditions through inference on the basis of the various parameters upon starting of machining of the workpiece.
In a preferred mode for carrying out the invention, the jump control apparatus for the electric discharge shaping/profiling machine may further include a machining stage detecting means for detecting a machining stage or status of the workpiece on the basis of a moving quantity of the main spindle. The machining conditions contain a plurality of preset values which differ in dependence on the machining stages. In this case, the numerical control unit may be so designed as to arithmetically determine the various parameters mentioned previously on the basis of the machining conditions corresponding to the machining stages or statuses, respectively.
In another preferred mode for carrying out the invention, the various parameters may include shape information of the tool electrode. In that case, the jump condition estimating unit may be comprised of a jump-up quantity estimating module designed for estimating a jump-up quantity of the tool electrode, and a jumping velocity estimating module designed for estimating a jumping velocity of the tool electrode.
In yet another preferred mode for carrying out the invention, the various parameters may include a spark gap between the tool electrode and the workpiece arithmetically determined on the basis of the machining conditions for the workpiece, and a machined-surface length extending from a machined surface being machined at a tip end of the tool electrode to a top surface of the workpiece. In this case, the jump-up quantity estimating module may be so designed as to estimate an optimal jump-up quantity for the tool electrode on the basis of the shape information of the tool electrode, the spark gap and the machined-surface length.
In still another preferred mode for carrying out the invention, the various parameters may include kinematic viscosity of the processing liquid. In this case, the jumping velocity estimating module may be so designed as to estimate the jumping velocity of the tool electrode required at a minimum on the basis of the kinematic viscosity of the processing liquid.
In still another preferred mode for carrying out the invention, the various parameters may include a spark gap between the tool electrode and the workpiece, a machined-surface length extending from a machined surface being machined at a tip end of the tool electrode to a top surface of the workpiece, an outer peripheral length of the tool electrode at the top surface of the workpiece, a machining area defined at the tip end of the tool electrode, kinematic viscosity of the processing liquid, and a constant indicating a ratio between an inertia force and a viscous force of the processing liquid. The above-mentioned constant may be set to a value greater than xe2x80x9c10xe2x80x9d in dependence on the jumping velocity of the tool electrode which is estimated by the jumping velocity estimating module. In that case, the jump-up quantity estimating module may be so designed as to estimate arithmetically an optimum jump-up quantity for the tool electrode on the basis of the various parameters in accordance with expression ju=dxc2x7hxc2x7L/S. On the other hand, the jumping velocity estimating module may be so designed as to estimate arithmetically the jumping velocity of the tool electrode required at a minimum on the basis of the various parameters in accordance with expression jmp=Rexc2x7Lxc2x7n/S.
In a further preferred mode for carrying out the invention, the various parameters may include a spark gap between the tool electrode and the workpiece, a machined-surface length extending from the machined surface being machined at a tip end of the tool electrode to a top surface of the workpiece, an outer peripheral length of the tool electrode at the top surface of the workpiece, a tip end width of the tool electrode, kinematic viscosity of the processing liquid, and a constant indicating a ratio between an inertia force and a viscous force of the processing liquid. The above-mentioned constant may be set to a value greater than xe2x80x9c10xe2x80x9d in dependence on the jumping velocity of the tool electrode which is estimated by the jumping velocity estimating module. In the case where the tool electrode is of a rib-like shape, the jump-up quantity estimating module may be so designed as to estimate arithmetically an optimum jump-up quantity for the tool electrode on the basis of the various parameters in accordance with expression ju=2dxc2x7h/w, while the jumping velocity estimating module may be so designed as to estimate arithmetically the jumping velocity of the tool electrode required at a minimum on the basis of the various parameters in accordance with expression jmp=2Rexc2x7n/w.
By virtue of the arrangements described above, the machining precision can be significantly improved with the machining time being remarkably shortened because the sludge produced in the course of the machining process can be discharged or removed speedily and timely in a satisfactory manner regardless of differences in the shape among the workpieces subjected to the machining process.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.